A team of scientists from the Department of Energy’s Oak Ridge National Laboratory (ORNL) and the University of Florida have developed a concept that they say could yield lower-cost, higher-efficiency systems for water heating in residential buildings.

The team's “semi-open” natural gas-fired design reduces the cost and complexity of traditional closed gas-fired systems by streamlining, and even eliminating, certain components.

For starters, the design combines water heating and dehumidification functions, which are typically found in separate architectures. A novel absorber device acts in place of the traditional evaporator component, pulling water vapor directly from the air through a membrane into a liquid solution. As the vapor is absorbed, much of the heat is transferred to domestic hot water.

The gas-fired heat pump water heater replaces the traditional evaporator. Image credit: ORNL. “When applied, the new concept could result in better than 100% energy efficiency because the system draws energy from the surrounding air as well as from the natural gas,” says Dr. Kyle Gluesenkamp, a researcher in ORNL's Building Equipment Group.

The simplified semi-open system would operate at the surrounding atmospheric pressure using an inexpensive, non-sealed solution pump. According to ORNL, this approach eliminates the need for the vacuum pumps found in closed systems that purge gas buildup. It also allows manufacturers to consider lower-cost, lightweight polymers instead of costly, bulkier metals to build equipment, making it less susceptible to corrosion.

Gluesenkamp says the semi-open architecture could be the basis for ultra-efficient heat pump water heaters that become commercially available "in a few years" to homeowners seeking to replace their existing gas water heater.

University of Florida researchers are now leading the development of a semi-open gas-fired heat pump prototype to evaluate the technology's commercial potential.